Fuel cells produce electrical energy by processing first and second reactants. Typically, this is through oxidation of hydrogen and reduction of oxygen. Because a plurality of fuel cells, when configured into a “stack,” can provide suitable voltage for powering a vehicle, there is an ongoing need for improved ways to provide reactants to automotive fuel cells.
High pressure hydrogen storage systems are one way of meeting this need. In such systems, hydrogen gas is compressed to 35 MPa (350 bar/5,000 psi) or 70 MPa (700 bar/10,000 psi) and stored in steel or lightweight composite tanks. While a variety of storage systems for gases are known (for example, medical gases, industrial gases, natural gas, and scuba tanks), high pressure hydrogen storage systems for automotive applications have challenges. For example, such systems must have components—regulators, sensors, couplings, valves, fuel lines, tanks, connectors, and sealing systems therefore—that operate under high pressure, low temperatures, high temperatures, corrosive conditions (storage is typically under the vehicle body), and over a long lifetime. Additionally, components of an automotive application must fit into a relatively limited space, so clearances between components are tight and replacement can be difficult. Moreover, because such systems are in vehicles, components must be reliably resistant to leakage of high pressure gaseous fuels.
One way to help manage leakage of high pressure gases is through the use of O-rings. An O-ring is typically an elastomeric material set into a groove formed within a first connector body (such as a cylinder surface) and compressed between the first connector body and a surface of a second connector body (such as an inner surface of a housing). The compression and the acting pressure deform the O-ring and create a seal between the first and second connector bodies. However, pressure forces acting upon the O-ring can cause its extrusion into gaps existing between the first and second connector bodies. Such gaps are primarily generated by manufacturing tolerances and design requirements, and the degree of extrusion is a function of O-ring hardness, clearance of mating parts, fluid/gas pressure, and temperature.
Because O-ring extrusion is a common cause of seal failure in pressurized systems, a back-up ring made of a relatively stiff material is typically also inserted into the groove of the first connector body. The back-up ring is typically installed at a portion of the groove opposite the source of pressure, and the O-ring is installed adjacent thereto, closest to the source of pressure. In such a configuration, pressure acts upon the O-ring, which exerts force on the back-up ring and causes it to extend past the edge of the groove and contact the second connector body, thereby bridging gaps between the first and second connector bodies and preventing extrusion of the O-ring into such gaps. In most applications, conventional back-up rings can allow for relatively large manufacturing tolerances between the mating surfaces of the first and second connector bodies because such rings bridges the gap between the mating parts
Conventional back-up rings are available in solid (uncut), single turn (scarf cut), and multi-turn (spiral cut) configurations, and examples of where such back-up rings are typically used include fitting-to-fitting connections, fitting-to-housing connections, pipe-to-fitting connections, and valve applications (such as valve shuttles, piston seals, valve seats, and valve housings).
High pressure hydrogen storage systems for automotive applications, and in particular for 70 MPa systems, are a relatively new technology in which the discovery of a variety of unique issues and challenges is ongoing during development. Among them is the discovery that conventional O-ring/back-up ring systems widely used in lower pressure applications and in industrial high-pressure applications are susceptible to failure in 70 MPa automotive applications. Such failure can arise due to O-ring extrusion into gaps existing between a conventional back-up ring and the inner circumference of a groove of a connector body (i.e., a gap within the groove itself rather than between the first and second connector bodies). This gap is determined by, among other things, the manufacturing tolerances of the connector body diameter, inner groove diameter, and back-up ring width. O-ring extrusion of this type is not an issue encountered in industrial high pressure applications where the ratio of seal area and gap size is comparatively large as compared to that in automotive applications. O-ring extrusion of this type is also not an issue encountered in lower pressure applications, where wider manufacturing tolerances are acceptable.
In light of the aforementioned, there exists a need for new ways of sealing between two connector bodies, including those of high pressure automotive systems. More particularly, there is a demonstrated need for O-ring/back-up ring sealing systems that overcome the shortcomings of the prior art.